Hydrogen transmission pipeline steel L245MH and production method thereof

Abstract

The invention relates to hydrogen transmission pipeline steel L245MH and a production method thereof, and belongs to the technical field of production of hot-rolled coil plates for transmission pipelines, and the hydrogen transmission pipeline steel L245MH comprises the following chemical components in percentage by mass: 0.035 to 0.055 percent of C, 0.05 to 0.20 percent of Si, 0.60 to 0.90 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.0010 percent of S, less than or equal to 0.0012 percent of O, 0.020 to 0.040 percent of Als, 0.010 to 0.025 percent of Nb, 0.005 to 0.020 percent of Ti, 0.10 to 0.25 percent of Cr, 0.0045 to 0.0090 percent of Ce, less than or equal to 0.0080 percent of N and the balance of Fe and inevitable impurities. By adopting the component design and combining a Ce alloying process under a vacuum condition and a carbide dispersion precipitation process under accelerated cooling, the obtained pipeline steel L245MH has good high-pressure hydrogen compatibility performance.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled coil production for transmission pipelines, and specifically relates to a hydrogen transmission pipeline steel L245MH and a production method thereof. Background Art

[0003] During the service of long-distance hydrogen pipelines, the pipes are in a high-pressure hydrogen-rich environment. Hydrogen can easily enter the metal and cause hydrogen embrittlement and hydrogen corrosion. The plasticity, toughness, and fatigue properties of existing pipeline steel materials will be significantly deteriorated, seriously affecting the long-term safe service of the pipeline. In the current actual engineering design material selection, medium and low-grade steel pipes of L245 to L360 are generally preferred.

[0004] Chinese patent CN114645215B announced "A L245S hydrogen-doped pipeline steel and its production method". Its product is produced using an online quenching + offline tempering process. The steel plate needs to be tempered after it comes off the line. Compared with hot-rolled coils, the process flow is long, the process cost is high, and the steel plate delivery cycle is long, which affects the efficiency of pipeline project construction. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a hydrogen pipeline steel L245MH and a production method thereof. The steel adopts a low C, Mn, P, and S component design, and adds trace amounts of stable carbide-forming elements such as Nb and Ti and rare earth element Ce. It is produced by slab slow cooling and TPMCP thermomechanical rolling process, so that the coil has not only conventional mechanical properties such as tensile and impact required by standard GB / T9711-2023, but also good high-pressure hydrogen compatibility performance.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: A hydrogen pipeline steel L245MH has the following chemical components and mass percentages: C: 0.035-0.055%, Si: 0.05-0.20%, Mn: 0.60-0.90%, P≤0.012%, S≤0.0010%, O≤0.0012%, Als: 0.020-0.040%, Nb: 0.010-0.025%, Ti: 0.005-0.020%, Cr: 0.10-0.25%, Ce: 0.0045-0.0090%, N≤0.0080%, and the remainder is Fe and unavoidable impurities; wherein the mass percentages of the three elements Ce, S and O satisfy the relationship: Ce / (S+O)≥3.5.

[0007] Furthermore, the hydrogen pipeline steel L245MH smooth sample was subjected to slow strain rate tensile test in pure hydrogen and pure nitrogen environment at 2.5-6.3 MPa, and the hydrogen embrittlement sensitivity coefficient K represented by elongation after fracture and reduction of cross section was obtained. H1 and K H2 All ≤0.10.

[0008] Furthermore, the microstructure type of the hydrogen pipeline steel L245MH is ferrite + pearlite, the ferrite area accounts for ≥92%, and the ferrite grain size is ≥9.5; the product thickness specification is 6 to 22.5 mm, and the width specification is 900 to 2150 mm.

[0009] Furthermore, the yield strength R of the hydrogen pipeline steel L245MH in the room temperature tensile test is t0.5 245~415MPa, tensile strength R m 415~585MPa, yield strength ratio R t0.5 / R m ≤0.85.

[0010] The production method of the hydrogen pipeline steel L245MH comprises the steps of molten steel smelting and refining outside the furnace, slab continuous casting, slab slow cooling, slab heating, thermomechanical rolling, cooling and coiling; Molten steel smelting and refining process outside the furnace: adopt LF-RH dual refining path, RH vacuum cycle at 0-1.0mbar for 15-25min, make the molten steel O content ≤0.0008%, H content ≤0.00015%, then increase the vacuum degree to 80-200mbar and add iron-cerium alloy, keep the vacuum degree and continue to cycle for 8-12min before ending, and let the molten steel stand for 20-40min; Cooling process: Laminar cooling adopts the front-end concentrated accelerated cooling mode, that is, the cooling water of groups 1 to n is turned on, and the cooling water flow of group a is (1.1) a-1 ×L1, 1≤a≤n, L1 is the flow rate of the first group of water.

[0011] Furthermore, in the molten steel smelting and off-furnace refining process, pre-desulfurization is carried out before the molten iron is charged into the furnace, and the S content of the molten iron after desulfurization is ≤0.0060%; the C content at the end of converter blowing is 0.020-0.035%; and the S content of the molten steel leaving the LF refining station is ≤0.0010%.

[0012] Furthermore, in the slab continuous casting process, the slab specifications are 230-260 mm in thickness and 1000-2200 mm in width; the section where the slab solidification end is located and the three sections before it are each pressed down by 1.5-2.0 mm.

[0013] Furthermore, in the slab slow cooling process, the off-line slabs are centrally stacked and slowly cooled, and the surface temperature of the slabs is ≥200°C after 48 hours of slow cooling.

[0014] Furthermore, the slab heating process is performed by heating the slab in a heating furnace for 160 to 240 minutes, and the furnace exit temperature is 1200±30°C.

[0015] Furthermore, the thermomechanical rolling process adopts a two-stage rolling process of rough rolling + finishing rolling; the finishing rolling is rolling in the austenite non-recrystallization zone, after 5 to 7 rolling passes, the final rolling temperature is 850±20°C; the coiling temperature of the coiling process is 520±20°C.

[0016] Compared with similar technologies, the innovative features and technical effects of the present invention include: (1) Low hydrogen embrittlement sensitivity composition design. Compared with ordinary pipeline steels of the same steel grade, the hydrogen pipeline steel L245MH of the present invention adopts a composition system design with low C, Mn, P, S and appropriate amounts of Nb, Ti, and Cr micro-alloying, especially adding a trace amount of rare earth element Ce. The addition of Ce on the basis of low P, S, H, and O control significantly reduces the hydrogen embrittlement sensitivity of steel, which is specifically reflected in: ① The diffusion activation energy of hydrogen in the steel matrix is ​​increased, thereby slowing down the diffusion rate of hydrogen into the steel; ② On the one hand, it reduces the activity of elements such as C, Nb, and Ti in the steel, hinders the premature precipitation of carbides such as NbC in the austenite region, thereby promoting the fine and dispersed precipitation of carbides in the ferrite transformation stage, and on the other hand, it combines with residual S in the steel to form fine and evenly distributed inclusions, reducing the number of long strips of large-sized MnS inclusions, both of which increase the number of hydrogen traps in the steel and reduce the enriched hydrogen content in the traps; ③ Combining with residual P in the steel to form CeP reduces the segregation of phosphorus at the grain boundary and improves the low-temperature toughness of the steel. The low hydrogen embrittlement sensitivity component design of the present invention can effectively slow down the diffusion of hydrogen into the steel matrix during the service of the hydrogen pipeline and inhibit the generation of hydrogen-induced cracking inside the pipe body.

[0017] (2) Ce alloying process under vacuum deep degassing conditions. After deep degassing of O and H in the refining RH process, a weak vacuum environment is maintained to add iron-cerium alloy to the molten steel. After stirring evenly, the molten steel is left to stand, which reduces the contact reaction between Ce and the molten steel and O and H in the air, reduces the amount of Ce oxide inclusions and hydrides generated, and avoids the high-melting point rare earth oxide inclusions that cannot fully float up and affect the cleanliness of the molten steel, thereby enhancing the effect of Ce microalloying on improving the low-temperature toughness and hydrogen embrittlement sensitivity of steel.

[0018] (3) Carbide dispersion precipitation process under accelerated cooling. In the cooling stage after rolling, concentrated cooling is adopted in the front section, and the flow rate of each group of water gradually increases from front to back, so that the ferrite transformation temperature is reduced. The high degree of supercooling increases the ferrite nucleation rate and ensures the formation of uniform and fine ferrite structure. At the same time, accelerated cooling prevents the premature precipitation of carbides during cooling, and it is easier to generate fine and dispersed nano-scale precipitates in the grain or grain boundary. The effect of the two increases the density of hydrogen traps at the phase boundary, thereby reducing the hydrogen embrittlement sensitivity of the steel.

[0019] The beneficial effects of the above technical solution are as follows: the hydrogen pipeline steel L245MH produced by the present invention meets the conventional properties of L245M specified in GBT 9711-2023 and GBT 14164-2013 (including room temperature tensile test, Charpy impact test, drop hammer test, etc.), and the elongation and cross-sectional shrinkage of the smooth sample in the slow strain rate tensile test under 2.5-6.3MPa pure hydrogen environment are close to the test results of pure nitrogen, and the hydrogen embrittlement sensitivity coefficient K H ≤0.10, with good hydrogen compatibility. The product can be used for processing and manufacturing steel pipes for pure hydrogen / hydrogen-blended pipeline transportation systems, providing high-quality raw materials for national clean energy transportation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a typical microstructure diagram of the hot-rolled coil according to Example 1 of the present invention. DETAILED DESCRIPTION Example 1

[0021] The chemical composition and mass percentage of the hydrogen pipeline steel L245MH in this implementation are: C: 0.050%, Si: 0.07%, Mn: 0.61%, P: 0.009%, S: 0.0013%, O: 0.0011%, Als: 0.034%, Nb: 0.025%, Ti: 0.020%, Cr: 0.20%, Ce: 0.0089%, N: 0.0030%, and the balance is Fe and unavoidable impurities; among which Ce / (S+O)=3.71.

[0022] according to Figure 1 It can be seen that its microstructure type is ferrite + a small amount of pearlite (the other embodiment drawings are similar, so they are omitted), the ferrite grain size is 10, the area accounts for 92%, the product thickness specification is 22.5mm, and the width specification is 1110mm. The yield strength R of the room temperature tensile test t0.5 The tensile strength is 295MPa and the m is 421MPa, and the yield strength ratio R t0.5 / R m is 0.70.

[0023] The production method of hydrogen pipeline steel L245MH in this embodiment includes molten steel smelting and refining outside the furnace, slab continuous casting, slab slow cooling, slab heating, thermomechanical rolling, cooling and coiling processes; the specific process steps are as follows: (1) Molten steel smelting and refining outside the furnace: The molten iron is pre-desulfurized before loading into the furnace. The sulfur content of the molten iron is 0.005% after desulfurization. The carbon content at the end of converter blowing is 0.035%. The refining adopts the LF-RH double refining path. The sulfur content of the molten steel out of the LF refining station is 0.0009%. The RH is vacuum circulated at 0.7 mbar for 16 minutes. The O content of the molten steel is 0.0008% and the H content is 0.00011%. Then the vacuum degree is increased to 175 mbar and ferrocerium alloy is added. The vacuum degree is maintained for another 11 minutes before the end. The molten steel is left to stand for 20 minutes. (2) Slab continuous casting: Slab thickness is 240 mm and width is 1200 mm. During casting, the solidification end of the slab is at the 8th section of the second cooling section, and the reduction amount of each section from 5 to 8 is 2 mm. (3) Slab slow cooling: The off-line slabs are stacked and slowly cooled. The surface temperature of the slabs is measured to be 294°C after 48 hours of slow cooling. (4) Slab heating: After slow cooling, the slab is placed in a heating furnace and heated for 226 minutes, with a furnace temperature of 1217°C. (5) Thermomechanical rolling: The slabs out of the furnace are rolled in two stages: rough rolling and finishing rolling. The intermediate slab thickness is 62 mm, the finishing rolling inlet temperature is 955 °C, the finishing rolling is 7 passes, and the final rolling temperature is 831 °C. (6) Layer cooling: adopt the front-end centralized accelerated cooling mode, open 8 groups of cooling water, the cooling water flow rates of groups 1 to 8 are 500, 550, 605, 666, 732, 805, 886, 974m 3 / min; (7) Coiling: Coiling temperature 500°C. Example 2

[0024] The chemical composition and mass percentage of the hydrogen pipeline steel L245MH in this implementation are: C: 0.055%, Si: 0.18%, Mn: 0.89%, P: 0.011%, S: 0.0004%, O: 0.0008%, Als: 0.025%, Nb: 0.025%, Ti: 0.013%, Cr: 0.16%, Ce: 0.0045%, N: 0.0037%, and the balance is Fe and unavoidable impurities; among which Ce / (S+O)=3.75.

[0025] The microstructure type of the hydrogen pipeline steel L245MH in this implementation is ferrite + a small amount of pearlite, the ferrite grain size is 9.5, the area accounts for 94%, the product thickness specification is 18.4mm, and the width specification is 900mm. The yield strength R of the room temperature tensile testt0.5 The tensile strength is 312MPa and R m is 415MPa, and the yield strength ratio R t0.5 / R m is 0.75.

[0026] The production method of hydrogen pipeline steel L245MH in this embodiment includes molten steel smelting and refining outside the furnace, slab continuous casting, slab slow cooling, slab heating, thermomechanical rolling, cooling and coiling processes; the specific process steps are as follows: (1) Molten steel smelting and refining outside the furnace: The molten iron is pre-desulfurized before loading into the furnace. The sulfur content of the molten iron is 0.005% after desulfurization. The carbon content at the end of converter blowing is 0.026%. The refining adopts the LF-RH double refining path. The sulfur content of the molten steel discharged from the LF refining station is 0.0004%. The RH is vacuum circulated at 0.1 mbar for 25 minutes. The O content of the molten steel is 0.0005% and the H content is 0.00010%. Then the vacuum degree is increased to 181 mbar and ferrocerium alloy is added. The vacuum degree is maintained for another 8 minutes before the end. The molten steel is left to stand for 25 minutes. (2) Slab continuous casting: Slab thickness is 240 mm and width is 1000 mm. During casting, the solidification end of the slab is at the 10th section of the secondary cooling section, and the reduction amount of each section from 7 to 10 is 1.5 mm. (3) Slab slow cooling: The slabs off the production line are stacked and slowly cooled. The surface temperature of the slabs is measured to be 227°C after 48 hours of slow cooling. (4) Slab heating: After slow cooling, the slab is placed in a heating furnace and heated for 240 minutes, with the exit temperature at 1230°C. (5) Thermomechanical rolling: The slabs out of the furnace are rolled in two stages: rough rolling and finishing rolling. The intermediate slab thickness is 70 mm, the finishing rolling inlet temperature is 988 °C, the finishing rolling adopts 7 passes, and the final rolling temperature is 870 °C. (6) Layer cooling: adopt the front-end centralized accelerated cooling mode, open 8 groups of cooling water, the cooling water flow rates of groups 1 to 8 are 450, 495, 545, 599, 659, 725, 797, and 877 m 3 / min; (7) Coiling: Coiling temperature 527℃. Example 3

[0027] The chemical composition and mass percentage of the hydrogen pipeline steel L245MH in this implementation are: C: 0.036%, Si: 0.12%, Mn: 0.90%, P: 0.012%, S: 0.0015%, O: 0.0006%, Als: 0.030%, Nb: 0.019%, Ti: 0.013%, Cr: 0.13%, Ce: 0.0080%, N: 0.0047%, and the balance is Fe and unavoidable impurities; among which Ce / (S+O)=3.81.

[0028] The microstructure type of the hydrogen pipeline steel L245MH in this implementation is ferrite + a small amount of pearlite, the ferrite grain size is 9.5, the area accounts for 93%, the product thickness specification is 17.5mm, and the width specification is 1850mm. The yield strength R of the room temperature tensile test t0.5 The tensile strength is 356MPa, m is 462MPa, and the yield strength ratio R t0.5 / R m It is 0.77.

[0029] The production method of hydrogen pipeline steel L245MH in this embodiment includes molten steel smelting and refining outside the furnace, slab continuous casting, slab slow cooling, slab heating, thermomechanical rolling, cooling and coiling processes; the specific process steps are as follows: (1) Molten steel smelting and refining outside the furnace: The molten iron is pre-desulfurized before loading into the furnace. The sulfur content of the molten iron is 0.004% after desulfurization. The carbon content at the end of converter blowing is 0.020%. The refining adopts the LF-RH double refining path. The sulfur content of the molten steel out of the LF refining station is 0.0010%. The RH is vacuum circulated at 0.7 mbar for 22 minutes. The O content of the molten steel is 0.0008% and the H content is 0.00014%. Then the vacuum degree is increased to 80 mbar and ferrocerium alloy is added. The vacuum degree is maintained for another 9 minutes before the end. The molten steel is left to stand for 38 minutes. (2) Slab continuous casting: Slab thickness is 250 mm and width is 1900 mm. During casting, the solidification end of the slab is at the 9th section of the secondary cooling section, and the reduction amount of each section from 6 to 9 is 1.7 mm. (3) Slab slow cooling: The off-line slabs are stacked and slowly cooled. The surface temperature of the slabs is measured to be 219°C after 48 hours of slow cooling. (4) Slab heating: After slow cooling, the slab is placed in a heating furnace and heated for 231 minutes, with a furnace temperature of 1224°C. (5) Thermomechanical rolling: The slabs out of the furnace are rolled in two stages: rough rolling and finishing rolling. The intermediate slab thickness is 65 mm, the finishing rolling inlet temperature is 1020 °C, the finishing rolling adopts 7 passes, and the final rolling temperature is 870 °C; (6) Layer cooling: adopt the front-end centralized accelerated cooling mode, open 8 groups of cooling water, the cooling water flow rates of groups 1 to 8 are 600, 660, 726, 799, 878, 966, 1063, 1169 m 3 / min; (7) Coiling: Coiling temperature 536°C. Example 4

[0030] The chemical composition and mass percentage of the hydrogen pipeline steel L245MH in this implementation are: C: 0.054%, Si: 0.20%, Mn: 0.71%, P: 0.011%, S: 0.0010%, O: 0.0008%, Als: 0.020%, Nb: 0.014%, Ti: 0.005%, Cr: 0.19%, Ce: 0.0090%, N: 0.0051%, and the balance is Fe and unavoidable impurities; among which Ce / (S+O)=5.00.

[0031] The microstructure type of the hydrogen pipeline steel L245MH in this implementation is ferrite + a small amount of pearlite, the ferrite grain size is 10.5, the area accounts for 95%, the product thickness specification is 14.5mm, and the width specification is 2150mm. The yield strength R of the room temperature tensile test t0.5 The tensile strength is 379MPa and the m is 446MPa, and the yield strength ratio R t0.5 / R m is 0.85.

[0032] The production method of hydrogen pipeline steel L245MH in this embodiment includes molten steel smelting and refining outside the furnace, slab continuous casting, slab slow cooling, slab heating, thermomechanical rolling, cooling and coiling processes; the specific process steps are as follows: (1) Molten steel smelting and refining outside the furnace: The molten iron is pre-desulfurized before loading into the furnace. The sulfur content of the molten iron is 0.005% after desulfurization. The carbon content at the end of converter blowing is 0.028%. The refining adopts the LF-RH double refining path. The sulfur content of the molten steel out of the LF refining station is 0.0005%. The RH is vacuum circulated at 0.8 mbar for 15 minutes. The O content of the molten steel is 0.0007% and the H content is 0.00014%. Then the vacuum degree is increased to 160 mbar and ferrocerium alloy is added. The vacuum degree is maintained for another 11 minutes before the end. The molten steel is left to stand for 27 minutes. (2) Slab continuous casting: Slab thickness is 230 mm and width is 2200 mm. During casting, the solidification end of the slab is at the 7th section of the secondary cooling section, and the reduction amount of each section from 4 to 7 is 2 mm. (3) Slab slow cooling: The off-line slabs are stacked and slowly cooled. The surface temperature of the slabs is measured to be 242°C after 48 hours of slow cooling. (4) Slab heating: After slow cooling, the slab is placed in a heating furnace and heated for 181 minutes, with a furnace temperature of 1211°C. (5) Thermomechanical rolling: The slabs out of the furnace are rolled in two stages: rough rolling and finishing rolling. The intermediate slab thickness is 67 mm, the finishing rolling inlet temperature is 994 °C, the finishing rolling is 7 passes, and the final rolling temperature is 842 °C. (6) Layer cooling: adopt the front-end centralized accelerated cooling mode, open 7 groups of cooling water, the cooling water flow rates of groups 1 to 7 are 650, 715, 787, 865, 878, 952, and 1047 m 3 / min; (7) Coiling: Coiling temperature 524°C. Example 5

[0033] The chemical composition and mass percentage of the hydrogen pipeline steel L245MH in this implementation are: C: 0.042%, Si: 0.12%, Mn: 0.74%, P: 0.010%, S: 0.0006%, O: 0.0010%, Als: 0.035%, Nb: 0.012%, Ti: 0.018%, Cr: 0.20%, Ce: 0.0077%, N: 0.0055%, and the balance is Fe and unavoidable impurities; among which Ce / (S+O)=4.81.

[0034] The microstructure type of the hydrogen pipeline steel L245MH in this implementation is ferrite + a small amount of pearlite, the ferrite grain size is grade 11, the area accounts for 96%, the product thickness specification is 12mm, and the width specification is 1390mm. The yield strength R of the room temperature tensile test t0.5 The tensile strength R is 362MPa. m is 447MPa, and the yield strength ratio R t0.5 / R m It is 0.81.

[0035] The production method of hydrogen pipeline steel L245MH in this embodiment includes molten steel smelting and refining outside the furnace, slab continuous casting, slab slow cooling, slab heating, thermomechanical rolling, cooling and coiling processes; the specific process steps are as follows: (1) Molten steel smelting and refining outside the furnace: The molten iron is pre-desulfurized before loading into the furnace. The sulfur content of the molten iron is 0.005% after desulfurization. The carbon content at the end of converter blowing is 0.031%. The refining adopts the LF-RH double refining path. The sulfur content of the molten steel discharged from the LF refining is 0.0006%. The RH is vacuum circulated at 0.4 mbar for 17 minutes. The O content of the molten steel is 0.0008% and the H content is 0.00015%. Then the vacuum degree is increased to 200 mbar and ferrocerium alloy is added. The vacuum degree is maintained for another 10 minutes before the end. The molten steel is left to stand for 40 minutes. (2) Slab continuous casting: Slab thickness is 250 mm and width is 1550 mm. During casting, the solidification end of the slab is at the 10th section of the secondary cooling section, and the reduction amount of each section from 7 to 10 is 2.0 mm. (3) Slab slow cooling: The off-line slabs are stacked and slowly cooled. The surface temperature of the slabs is measured to be 252°C after 48 hours of slow cooling. (4) Slab heating: After slow cooling, the slab is placed in a heating furnace and heated for 230 minutes, with the exit temperature reaching 1186°C. (5) Thermomechanical rolling: The slabs out of the furnace are rolled in two stages: rough rolling and finishing rolling. The intermediate slab thickness is 65 mm, the finishing rolling inlet temperature is 1007 °C, the finishing rolling adopts 6 passes, and the final rolling temperature is 830 °C. (6) Layer cooling: adopt the front-end centralized accelerated cooling mode, open 7 groups of cooling water, the cooling water flow rates of groups 1 to 7 are 500, 550, 605, 666, 732, 805, and 886 m3 respectively. 3 / min; (7) Coiling: Coiling temperature 532°C. Example 6

[0036] The chemical composition and mass percentage of the hydrogen pipeline steel L245MH in this implementation are: C: 0.035%, Si: 0.05%, Mn: 0.62%, P: 0.008%, S: 0.0012%, O: 0.0012%, Als: 0.027%, Nb: 0.010%, Ti: 0.012%, Cr: 0.10%, Ce: 0.0084%, N: 0.0080%, and the balance is Fe and unavoidable impurities; among which Ce / (S+O)=3.5.

[0037] The microstructure type of the hydrogen pipeline steel L245MH in this implementation is ferrite + a small amount of pearlite, the ferrite grain size is 11.5, the area accounts for 94%, the product thickness specification is 10mm, and the width specification is 1550mm. The yield strength R of the room temperature tensile test t0.5 The tensile strength is 344MPa, m is 441MPa, and the yield strength ratio R t0.5 / R m It is 0.78.

[0038] The production method of hydrogen pipeline steel L245MH in this embodiment includes molten steel smelting and refining outside the furnace, slab continuous casting, slab slow cooling, slab heating, thermomechanical rolling, cooling and coiling processes; the specific process steps are as follows: (1) Molten steel smelting and refining outside the furnace: The molten iron is pre-desulfurized before loading into the furnace. The sulfur content of the molten iron is 0.006% after desulfurization. The carbon content at the end of converter blowing is 0.025%. The refining adopts the LF-RH double refining path. The sulfur content of the molten steel out of the LF refining station is 0.0010%. The RH is vacuum circulated at 0.1 mbar for 16 minutes. The O content of the molten steel is 0.0007% and the H content is 0.00013%. Then the vacuum degree is increased to 124 mbar and ferrocerium alloy is added. The vacuum degree is maintained for another 8 minutes before the end. The molten steel is left to stand for 33 minutes. (2) Slab continuous casting: Slab thickness is 260 mm and width is 1650 mm. During casting, the solidification end of the slab is at the 10th section of the secondary cooling section, and the reduction amount of each section from 7 to 10 is 1.8 mm. (3) Slab slow cooling: The off-line slabs are stacked and slowly cooled. The surface temperature of the slabs is measured to be 200°C after 48 hours of slow cooling. (4) Slab heating: After slow cooling, the slab is placed in a heating furnace and heated for 207 minutes, with a furnace temperature of 1170°C. (5) Thermomechanical rolling: The slabs out of the furnace are rolled in two stages: rough rolling and finishing rolling. The intermediate slab thickness is 68 mm, the finishing rolling inlet temperature is 950 °C, the finishing rolling adopts 6 passes, and the final rolling temperature is 865 °C. (6) Layer cooling: adopt the front-end centralized accelerated cooling mode, open 6 groups of cooling water, the cooling water flow rates of groups 1 to 6 are 550, 605, 666, 732, 805, and 886 m3 respectively. 3 / min; (7) Coiling: Coiling temperature 540°C. Example 7

[0039] The chemical composition and mass percentage of the hydrogen pipeline steel L245MH in this implementation are: C: 0.040%, Si: 0.09%, Mn: 0.60%, P: 0.006%, S: 0.0008%, O: 0.0009%, Als: 0.040%, Nb: 0.010%, Ti: 0.019%, Cr: 0.14%, Ce: 0.0060%, N: 0.0053%, and the balance is Fe and unavoidable impurities; among which Ce / (S+O)=3.53.

[0040] The microstructure type of the hydrogen pipeline steel L245MH in this implementation is ferrite + a small amount of pearlite, the ferrite grain size is 10.5, the area accounts for 93%, the product thickness specification is 6mm, and the width specification is 1210mm. The yield strength R of the room temperature tensile test t0.5 The tensile strength is 413MPa, m is 581MPa, and the yield strength ratio R t0.5 / R m It is 0.71.

[0041] The production method of hydrogen pipeline steel L245MH in this embodiment includes molten steel smelting and refining outside the furnace, slab continuous casting, slab slow cooling, slab heating, thermomechanical rolling, cooling and coiling processes; the specific process steps are as follows: (1) Molten steel smelting and refining outside the furnace: The molten iron is pre-desulfurized before loading into the furnace. The sulfur content of the molten iron is 0.005% after desulfurization. The carbon content at the end of converter blowing is 0.029%. The refining adopts the LF-RH double refining path. The sulfur content of the molten steel out of the LF refining station is 0.0008%. The RH is vacuum circulated at 0.3 mbar for 21 minutes. The O content of the molten steel is 0.0008% and the H content is 0.00013%. Then the vacuum degree is increased to 118 mbar and ferrocerium alloy is added. The vacuum degree is maintained for another 12 minutes before the end. The molten steel is left to stand for 32 minutes. (2) Slab continuous casting: Slab thickness is 250 mm and width is 1250 mm. During casting, the solidification end of the slab is at the 9th section of the secondary cooling section, and the reduction amount of each section from 6 to 9 is 1.5 mm. (3) Slab slow cooling: The off-line slabs are stacked and slowly cooled. The surface temperature of the slabs is measured to be 264°C after 48 hours of slow cooling. (4) Slab heating: After slow cooling, the slab is placed in a heating furnace and heated for 160 minutes, with the exit temperature reaching 1192°C. (5) Thermomechanical rolling: The slabs out of the furnace are rolled in two stages: rough rolling and finishing rolling. The intermediate slab thickness is 73 mm, the finishing rolling inlet temperature is 1020 °C, the finishing rolling is carried out in 5 passes, and the final rolling temperature is 838 °C. (6) Layer cooling: adopt the front-end centralized accelerated cooling mode, open 5 groups of cooling water, the cooling water flow rates of groups 1 to 8 are 500, 550, 605, 666, and 732 m 3 / min; (7) Coiling: Coiling temperature 532 °C.

[0042] The slow strain rate tensile test performance results of the smooth samples of each embodiment in pure hydrogen and pure nitrogen high pressure atmospheres are shown in Table 1 below.

[0043] Table 1. Performance results of slow tensile test of various examples

[0044] It can be seen from the above table that the elongation and cross-sectional shrinkage of the hydrogen pipeline steel L245MH product of the present invention in the slow strain rate tensile test in a pure hydrogen environment of 6.3 MPa are close to the test results in a pure nitrogen environment, and the hydrogen embrittlement sensitivity coefficient K H1 and K H2 Both are ≤0.10. The material has good hydrogen compatibility and can be used for the processing and manufacturing of steel pipes for hydrogen pipeline transportation systems.

Claims

1. A hydrogen pipeline steel L245MH, characterized in that: Its chemical composition and mass percentage are: C: 0.035-0.055%, Si: 0.05-0.20%, Mn: 0.60-0.90%, P≤0.012%, S≤0.0010%, O≤0.0012%, Als: 0.020-0.040%, Nb: 0.010-0.025%, Ti: 0.005-0.020%, Cr: 0.10-0.25%, Ce: 0.0045-0.0090%, N≤0.0080%, and the remainder is Fe and unavoidable impurities; among them, the mass percentages of the three elements Ce, S and O satisfy the relationship: Ce / (S+O)≥3.

5.

2. The hydrogen pipeline steel L245MH according to claim 1 is characterized in that: The smooth specimens were subjected to slow strain rate tensile tests in pure hydrogen and pure nitrogen environments at 2.5 to 6.3 MPa. The hydrogen embrittlement sensitivity coefficient K was characterized by elongation after fracture and reduction of area, respectively. H1 and K H2 All ≤0.

10.

3. The hydrogen pipeline steel L245MH according to claim 2 is characterized in that: Its microstructure type is ferrite + pearlite, the ferrite area accounts for ≥92%, and the ferrite grain size is ≥9.5; the product thickness specification is 6~22.5mm, and the width specification is 900~2150mm.

4. The hydrogen pipeline steel L245MH according to claim 3 is characterized in that: The yield strength R of the room temperature tensile test t0.5 245~415MPa, tensile strength R m 415~585MPa, yield strength ratio R t0.5 / R m ≤0.

85.

5. The production method of hydrogen pipeline steel L245MH according to any one of claims 1 to 4, characterized in that: It includes molten steel smelting and refining outside the furnace, slab continuous casting, slab slow cooling, slab heating, thermomechanical rolling, cooling, and coiling processes; Molten steel smelting and refining process outside the furnace: adopt LF-RH dual refining path, RH vacuum cycle at 0-1.0mbar for 15-25min, make the molten steel O content ≤0.0008%, H content ≤0.00015%, then increase the vacuum degree to 80-200mbar and add iron-cerium alloy, keep the vacuum degree and continue to cycle for 8-12min before ending, and let the molten steel stand for 20-40min; Cooling process: Laminar cooling adopts the front-end concentrated accelerated cooling mode, that is, the cooling water of groups 1 to n is turned on, and the cooling water flow of group a is (1.1) a-1 ×L1, 1≤a≤n, L1 is the flow rate of the first group of water.

6. The method for producing hydrogen pipeline steel L245MH according to claim 5, characterized in that: In the steel smelting and off-furnace refining process, pre-desulfurization is carried out before the molten iron is charged into the furnace. The S content of the molten iron is ≤0.0060% after desulfurization; the C content at the end of converter blowing is 0.020~0.035%; the S content of the molten steel leaving the LF refining station is ≤0.0010%.

7. The method for producing hydrogen pipeline steel L245MH according to claim 6, characterized in that: In the slab continuous casting process, the slab specifications are 230-260mm in thickness and 1000-2200mm in width; the section where the slab solidification end is located and the three sections before it are each pressed down by 1.5-2.0mm.

8. The method for producing hydrogen pipeline steel L245MH according to claim 7, characterized in that: In the slab slow cooling process, the slabs off the line are centrally stacked and slowly cooled. The surface temperature of the slabs is ≥200℃ after 48 hours of slow cooling.

9. The method for producing hydrogen pipeline steel L245MH according to any one of claims 1 to 8, characterized in that: The slab heating process is to heat in the heating furnace for 160 to 240 minutes, and the furnace temperature is 1200±30℃.

10. The method for producing hydrogen pipeline steel L245MH according to claim 9, characterized in that: The thermomechanical rolling process adopts two-stage rolling of rough rolling + finishing rolling; the finishing rolling is rolling in the austenite non-recrystallization zone, after 5 to 7 rolling passes, the final rolling temperature is 850±20℃; the coiling temperature of the coiling process is 520±20℃.

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